A circularly polarizing plate has been used in an image display apparatus such as a liquid crystal display apparatus (LCD) or an organic electroluminescence display apparatus (OLED) for the purposes of improving its display characteristics and preventing reflection. The circularly polarizing plate is typically obtained by laminating a polarizer and a retardation film (typically a λ/4 plate) so that the absorption axis of the polarizer and the slow axis of the retardation film may form an angle of 45°. Hitherto, the retardation film has been typically produced by performing uniaxial stretching or biaxial stretching in a longitudinal direction and/or a lateral direction, and hence its slow axis is expressed in the lateral direction (widthwise direction) or longitudinal direction (lengthwise direction) of a raw film in many cases. As a result, in order to produce the circularly polarizing plate, it has been necessary to perform the following. The retardation film is cut so as to form an angle of 45° relative to its lateral direction or longitudinal direction, and the resultant pieces are bonded one by one.
To solve such problem, there has been proposed a technology involving performing stretching in an oblique direction to express the slow axis of the retardation film in the oblique direction (for example, Patent Literature 1). However, the stretching in the oblique direction involves the following problems: the direction of the slow axis of the retardation film to be obtained deviates from a preset value (typically becomes larger than the preset value) with time over a predetermined time period from the initial stage of the stretching; and even when the direction of the slow axis becomes constant after the predetermined time period, the variation of the direction periodically occurs along the lengthwise direction of the retardation film.